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Process Optimization Using On-line Continuous Zeta Potential Monitoring
Nano
Ana Morfesis, PhDMalvern Instruments, [email protected]
Water System Optimization ConferencePartnership for Safe Water - AWWAHershey, PA
October 30, 2015
Coagulation Control in Water Treatment• Impurities in Wastewater are mostly Anionic
• Minerals• Organics• Domestic Sewage• Industrial Waste• Ecoli, Cryptosporidium and Giardia
• Cationic additives have been developed to neutralize chargeHigh Zeta Potential Low or Zero Zeta Potential
Unstable suspensionStable suspension
Introduction – Impurities and Changes Raw Water Contains a Multitude of Impurities
Introduction• Flocculation Chemistry is optimized by addition of chemicals that
neutralize the charge of particles in suspension.
• But….MORE CHEMICALS ≠ BETTER FLOC
Introduction – The Problem with NOM Impurities
Organics vary with Source, Season and Runoff Events
*E.L. Sharp, NOM6 Sweden 2015 Conference
Coagulation Control in Water TreatmentCurrent coagulation performance monitoring methods include
• Turbidity – no indication of charge• Filter loading - no indication of charge• Jar / Floc test – slow, no indication of charge• Streaming current – low sensitivity and not specific• Zeta potential
Jar Test
Floc Test
Zeta Potential is NOT Streaming Current
Summary of differences in techniques
Streaming current Electrophoretic Light Scattering
Measures portion of particles that adsorb to cell walls
Measures all particles, organics and minerals directly
Calibration of output required
Absolute technique, no calibration required
The low concentration of particles in feed water leads to very low signal, therefore insensitive to small changes
Can measure at very low concentrations
Signal depends on the sample conductivity, which varies as the nature of the sample changes
Zeta potential is reported directly
Streaming Current Device
Measuring Zeta Potential
Electrophoresis = Particle Velocity/Electric Field Strength
Electrophoretic Light Scattering (ELS)Measured parameter is the frequency shift of the scattered light.
• Scattered light is frequency (Doppler) shifted• Frequency shift
f = 2 sin(/2)/ = the particle velocity = laser wavelength = scattering angle
• Frequency shifts determined by Fourier transformation and phase analysis light scattering
Setting a Zeta Potential operating range
Under dosing Over dosing
-10 +3
Optimum
-10mV +3mV
Increase Coagulant Reduce Coagulant
Under Dose Over DoseOptimum Dose
-5mV
Zeta optimization helps control Turbidity, NOM, DOC
Role of Zeta (ζ) Potential in the Optimization of Water Treatment FacilityOperations (Ind. Eng. Chem. Res. 2009, 48, 2305–2308)
New Mexico Facility – FeCl3
-20
-15
-10
-5
0
5
10
0
5
10
15
20
25
0 20 40 60 80 100
Zeta
Pot
entia
l, m
v
pH, T
urbi
dity
, UVA
FeCl3 Dose, mg/L
Zeta Tests at Reduced pH
pH
Turbidity
UV254
Zeta Potential
On-line Zetasizer WT
On-Line Zeta Measurements
• Based on Zetasizer Nano platform• Automated sampling and industrial controls• Malvern Link II - software for automation control
and integration into plant SCADA
• Coagulation is a critical step that effects the rest of the process• Incoming water can change rapidly • Plant impacts in less than an hour• Rapid detection of treatment events• Precise dosing = chemical optimization• Manpower optimization• Integration into plant control system• Enabling automatic dose control (future steps)
Why on-line?
Zetasizer WT
Evaluating coagulant impact ACH & Polymer
160 MGD plant in Northern Utah
Filtered Turbidity
Zeta
Flow
ACH
Polymer
Zeta Potential [mV]
Zeta potential and Ferric Sulphate
Data courtesy of Severn Trent Water
Ferric
Zp
Responding to changing conditions…
Data courtesy of Severn Trent Water
Organics
Zp
Turbidity
Ferric
Detecting a process upset…
Data courtesy of Tacoma Water Green River plant
Filtered Turbidity
Zeta
Early Access unit at Wemlinger plant, Aurora CO
• 80 MGD Direct Filtration Plant using lab Zetasizer since 2010• Plant relies on Zeta potential for dosing decisions since 2011
-3mV - +3mV optimal rangeLab Zeta measured once a shift
• Zetasizer WT system installed in 2012• On-line system - > 400 measurements per day• On-line results & Lab Zeta results match• Data exchange with plant control DeltaV system
via Modbus TCP/IP
- Members of the Partnership for Safe Water
- Awarded Excellence in Water Treatment Award, Partnership for Safe Water 2008
- Average annual Combined Filter Effluent Turbidity 0.023 NTU.
Direct Filtration Plant
Lab Zeta vs. On-line Zeta
-10.000
-8.000
-6.000
-4.000
-2.000
0.000
2.000
4.000
6.000
8.000
10.000
1/31/2013
2/10/2013
2/20/2013
3/2/2013
3/12/2013
3/22/2013
4/1/2013
4/11/2013
4/21/2013
5/1/2013
On-line Zeta
Lab Zeta
Wemlinger Water Purification Facility
Lab Zeta vs. On-line Zeta
-8.000
-6.000
-4.000
-2.000
0.000
2.000
4.000
6.000
8.000
10.000
5/26/2013
6/5/2013
6/15/2013
6/25/2013
7/5/2013
7/15/2013
7/25/2013
8/4/2013
On-line Zeta
Lab Zeta
Wemlinger Water Purification Facility
On-line dataZeta potential data used to stabilize the plant after PLC failure
Alum = 4.10 mg/l and Cationic polymer = 3.05 mg/l.
Alum = 3.65 mg/l and Cationic polymer = 2.75 mg/l
On-line data
Zeta potential data used to stabilize the plant after PLC failure
~12 hours
Observed negative effect of Rapid mixing
~17% reduction in dosing with mixer off!
Stable dose a few days after the event:Alum = 3.40 mg/l and Cationic polymer = 2.55 mg/l
Zeta vs. SCM
• On-line Zeta matches Lab Zeta• Streaming Current Monitor not showing shift to negative charge.
Aurora - Wemlinger Results› Addressing technology gap for coagulation control
› Enables unattended operation, automation of dosing control and man power optimization – future proofing.
› Significant savings in chemicals and less sludge
› Wemlinger plant ~20% cost savings by switching to zeta.› Improving plant stability, preventing breakthroughs and
extending filter operating times
2010 2011 2012 2013
Alum Costs$ 69,576.64 $55,870.98 $56,879.70 $34,466.31
PEC Cost$ 214,912.09 $72,709.90 $68,071.11 $56,685.22
Coag. Summary$ 284,488.73 $128,580.88 $124,950.81 $91,151.53
Cost per Million$32.55 $22.81 $18.43 $20.70*
MG Delivered8739.44 5636.47 6780.99 4402.88
*2013 numbers impacted by flooding
Wemlinger WPF
Published Results
Wemlinger Operators Say:› “Zeta potential provides a measurable and reliable value
indicating when a production issue occurs”
› “It provides better sensitivity and is a sharper indicator that the process has changed.”
› “This information helps our operators make informed decisions”
› “The on-line zeta measurement is a proactive tool for preventing treatment problems and keeping water processing plants operating smoothly.”
SummaryZeta potential measurements, 1st Principals, direct measurement
Not Calibrated Charge monitoring / zeta potential,
allows for precise control of coagulant dosing
Process; Conventional, Direct Filtration, HybridSize; 40 MGD – 160 MGDChemistry; Alum, ACH, Ferric Sulfate and Chloride, cationic polymers
• Significant cost savings were obtained
• Plant stability was often considered even more important.
“Severn Trent Water have been using the Malvern Zetasizer technology for over
5 years and currently use zeta potential to optimize the coagulant dose at several
of our water treatment works. I am a firm believer in this technology and have
welcomed the opportunity to work with Malvern Instruments and to support this
transition into an online arena - which has the potential to revolutionize
coagulation control within the Water Industry in the future.”
Emma Sharp, Water Treatment and Quality Lead, Severn Trent Water, UK
